1. Field of the Invention
The present invention relates to a high-pressure discharge lamp for use as a light source of optical equipment such as a liquid crystal projector, for example.
2. Description of the Related Art
Recently, for use as a light source of e.g. optical equipment, a high-pressure discharge lamp has been developed which has a relatively small gap between electrodes (arc length) for enhancing the luminance and light utilization efficiency. However, in a high-pressure discharge lamp of such a short arc type, the tip ends of the electrodes are heated to high temperature, resulting in evaporation of the electrodes. Therefore, when the lamp continues to be lit for a relatively long time, the electrodes are deformed, resulting in so-called arc jump (fluctuation of the luminous point of the electrodes), which causes a flicker.
Further, the evaporated material of the electrodes often adheres to the inner surface of the arc tube, whereby the arc tube is blackened. Furthermore, when the arc comes close to a wall surface of the arc tube due to the deformation of the electrodes, the arc tube may be heated to extremely high temperature.
As a measure to solve these problems, the gazette of JP-A-11-149899 discloses a technique in which the amount of mercury in the arc tube and the halogen gas concentration are optimized while K2O (potassium oxide) contained in the tungsten electrodes is suppressed to a value not more than 12 ppm for prolonging the lifetime of a high-pressure discharge lamp.
However, such suppression of the K2O content to prevent blackening of the arc is not sufficiently effective for preventing the deformation of electrodes, and hence, for preventing the arc jump.